Metagenomic Study of the Human oral Microbiota
Overview The human mouth contains hundreds of types of different bacteria, viruses, and fungi.These microorganisms can be either harmful or helpful to us. Interestingly, these organisms can form biofilms with each other, despite being of different species. Within the biofilm, they can send and receive signaling molecules from other organisms within the biofilm. The sharing of information can also lead to horizontal gene transfer, which can confer the resistance of certain antibiotics.These species are mostly commensal, which means that they benefit us and themselves. They can become opportunistic pathogens, however, if there is a significant change in the environment; such as hygiene. Metagenome To study a metagenome, the complete biome must be taken from different organisms of different species residing in the same environment (in this case, the human mouth). For this metagenomic study of the oral microbiome, 3 healthy human individuals had DNA from their mouth sequenced via high-throughput sequencing (2). This study was conducted by Lazarevic et al. The DNA that was studied was from the organisms that were living in the mouth of the individuals, such as the bacteria, fungi, viruses, and their own human cells (2). To prevent the human DNA from being sequenced, the Lazarevic group used primers that were specific to non-human organisms. There were over 1 million sequences that resulted from the DNA isolation, not including human cells. The most common phyla that resulted from this study were Firmicutes, Proteobacteria, Actinobacteria, Fusobacteria and TM7. All 5 of the most common phyla were different types of bacteria, albeit more gram positive than negative since the mouth is an aerobic environment. More bacteria was found to be present in the mouth than fungi or viruses (2). Oral Biofilms The bacteria that reside in the human mouth have a tendency to form biofilms within their host (1). A biofilm is a cluster of cells, of different species, that aggregate together by secreting adherent proteins (3). Within a biofilm, these microorganisms can send and receive signaling molecules to other cells within the biolfilm. Along with the sharing of signaling molecules, these cells can also undergo horizontal gene transfer; which is the sharing of DNA (mostly plasmids) between bacteria (3).Through this sharing of DNA, bacteria can gain genes that confer resistance to antibiotics that they were previously susceptible to. This is a major problem in hospitals with the increase in nosocomial pathogens gaining resistance to powerful antibiotics. The species within these biofilms can change depending on different environmental conditions, such as pH, nutrient concentrations or even temperature (1). The Oral Microbiome and Disease There have been many different metagenomic studies on the oral microbiome and its relationship to the development of oral diseases (4). These studies have had to the findings of different genes, more specifically metabolic pathways, that can lead to oral disease; such as the breakdown of excess glucose to acidic byproducts that lead to enamel/tooth decay. The gaining of a gene for a certain enzyme can turn a commensal oral organism into a harmful pathogen (4). References 1. The Oral Microbiota: Living with a Permanent Guest ''PMID: PMC2768665 2. ''Metagenomic study of the oral microbiota by Illumina high-throughput sequencing. ''PMID: 19796657 3. Wikipedia: ''Biofilms 4. Application of metagenomics in understanding oral health and disease. PMID: 24642489 5. IMAGE 1 6. IMAGE 2